670 



BELL SYSTEM TECHNICAL JOURNAL 



Asymmetrical Directivity Through Far End Terminations 

 Where it is desired to make an antenna responsive to signals in a 

 given direction but to discriminate against signals in the opposite direc- 

 tion, reflector systems are often employed. These reflectors may be 

 parasitic or they may be directly connected to the receiver through 

 apparatus controlling their phase and amplitude relations. Our ex- 

 perience has shown that reflectors may be employed in connection with 

 the type of antenna under consideration for the purpose of obtaining 

 unilateral directivity. However, the use of reflectors restricts the 

 possible frequency range, as they only function efficiently at specific 

 spacings in relation to the wave-length used. For this reason, reflec- 

 tors will not be discussed in this paper, although they are employed 

 where a broad frequency range is not essential. 



I 2 3 4 5 6 7 

 INDUCED ^ 



VOLTAGE ♦ * \ X -« - 



12 3 4 5 6 7 



CURRENT AT 



R-DIRECT 

 PROPAGATION 



RESULTANT 

 CURRENT 



.- V \ ♦ 



RESULTANT 

 CURRENT 



-v.» ^ ^ ^ 



CURRENT AT 

 R VIA 



TERMINATION 

 REFLECTION 



ZERO WHEN r = 2o 



ZERO WHEN r-Zo 



Fig. 11 — ^\'ector relations in an inverted \' antenna — asymmetrical directivity. 



Tilted wire antennas and their combinations are particularly adapted 

 to obtaining directional asymmetry through proper terminations of the 



